The proposed research project will examine in detail the effects of jejunoileal bypass and gastric bypass on the feeding and drinking behavior and body weight regulation of obese and lean rats. Both hypothalamic (VMH) obese and genetically (fatty) obese rats will be used. Specific experiments will examine the effects of bypass surgery on food and water intake, sweetness appetite, conditioned food aversion, feeding and drinking patterns, and ingestive responses to various homeostatic challenges. Other experiments will analyze the role of different segments of the intestinal tract in the anorexia and weight loss produced by intestinal bypass by utilizing various intestinal bypass, resection, transposition, and parabiotic-cross preparations. The objective of this research is to elucidate the mechanisms by which bypass surgery reduces appetite, food intake, and body weight in obese animals.